DUST AND THE TYPE II-PLATEAU SUPERNOVA 2004dj

We present mid-infrared (MIR) spectroscopy of a Type II-plateau supernova, SN\n2004dj, obtained with the Spitzer Space Telescope, spanning 106--1393 d after\nexplosion. MIR photometry plus optical/near-IR observations are also reported.\nAn early-time MIR excess is attributed to emission from non-silicate dust\nformed within a cool dense shell (CDS). Most of the CDS dust condensed between\n50 d and 165 d, reaching a mass of 0.3 x 10^{-5} Msun. Throughout the\nobservations much of the longer wavelength (>10 microns) part of the continuum\nis explained as an IR echo from interstellar dust. The MIR excess strengthened\nat later times. We show that this was due to thermal emission from warm,\nnon-silicate dust formed in the ejecta. Using optical/near-IR line-profiles and\nthe MIR continua, we show that the dust was distributed as a disk whose radius\nappeared to be slowly shrinking. The disk radius may correspond to a grain\ndestruction zone caused by a reverse shock which also heated the dust. The\ndust-disk lay nearly face-on, had high opacities in the optical/near-IR\nregions, but remained optically thin in the MIR over much of the period\nstudied. Assuming a uniform dust density, the ejecta dust mass by 996 d was 0.5\n+/- 0.1) x 10^{-4} Msun, and exceeded 10^{-4}Msun by 1393 d. For a dust density\nrising toward the center the limit is higher. Nevertheless, this study suggests\nthat the amount of freshly-synthesized dust in the SN 2004dj ejecta is\nconsistent with that found from previous studies, and adds further weight to\nthe claim that such events could not have been major contributors to the cosmic\ndust budget.\n